On 8/9/2016 4:13 PM, Jan Beulich wrote:
On 09.08.16 at 09:39, <yu.c.zh...@linux.intel.com> wrote:
On 8/9/2016 12:29 AM, Jan Beulich wrote:
On 12.07.16 at 11:02, <yu.c.zh...@linux.intel.com> wrote:
@@ -5512,6 +5513,12 @@ static int hvmop_set_mem_type(
if ( rc )
goto out;
+ if ( t == p2m_ram_rw && memtype[a.hvmmem_type] == p2m_ioreq_server )
+ p2m->ioreq.entry_count++;
+
+ if ( t == p2m_ioreq_server && memtype[a.hvmmem_type] == p2m_ram_rw )
+ p2m->ioreq.entry_count--;
+
These (and others below) happen, afaict, outside of any lock, which
can't be right.
How about we make this entry_count as atomic_t and use atomic_inc/dec
instead?
That's certainly one of the options, but beware of overflow.
Oh, thanks for your remind, Jan. I just found that atomic_t is defined
as "typedef struct { int counter; } atomic_t;"
which do have overflow issues if entry_count is supposed to be a uint32
or uint64.
Now I have another thought: the entry_count is referenced in 3
different scenarios:
1> the hvmop handlers - hvmop_set_mem_type() and
hvmop_map_mem_type_to_ioreq_server(),
which are triggered by device model, and will not be concurrent. And
hvmop_set_mem_type() will
permit the mem type change only when an ioreq server has already been
mapped to this type.
2> the misconfiguration handlers - resolve_misconfig() or do_recalc(),
which are triggered by HVM's
vm exit, yet this will only happen after the ioreq server has already
been unmapped. This means the
accesses to the entry_count will not be concurrent with the above hvmop
handlers.
3> routine hap_enable_log_dirty() - this can be triggered by tool stack
at any time, but only by read
access to this entry_count, so a read_atomic() would work.
Do you think this analysis reasonable?
If so, we may only use read_atomic() to get the value of entry_count in
hap_enable_log_dirty() and keep
other places as it is.
Of course, some explanation comments in entry_count's definition would
be necessary. :-)
Yu
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